As devices have become smaller and have increased inputs and/or outputs, wire bonding has been used. In wire bonding, a bond wire is used to electrically connect bond pads on a chip with conductive fingers. The conductive fingers provide an electrical connection external to a package.
FIG. 7 is a plan view of a portion of a conventional semiconductor device having bond wires connected to conductive fingers.
FIG. 8 is a side view of the bond wire and a capillary used for setting a bond wire in the conventional semiconductor device of FIG. 7.
Referring now to FIG. 7 in conjunction with FIG. 8, a conventional semiconductor device 60 includes a semiconductor chip 64, a substrate 68, and bond wires 70. Semiconductor chip 64 includes bond pads 62. Substrate 68 includes conductive fingers 66. Each bond pad 62 is connected to a respective conductive finger 66 with a bond wire 70.
Before a semiconductor chip 64 goes through a bonding step to manufacture the conventional semiconductor device 60, a probe step is typically executed. The probe step is executed to test functionality of the semiconductor chip 64. In the probing step, a probe needle (not shown) is brought into contact with surface of the center of each bond pad 62. The probe will generally leave a mark and affect the planarity of the surface of the bond pad 62. Then, in the bonding step, a capillary 72 is used to connect a bond wire 70 to the center of a bond pad 62. In this way, a bond pad 62 is connected to a conductive finger 66.
Bond pads 62 can be arranged in a line near the edge of semiconductor chip 64. Alternatively, bond pads 62 may also be arranged in a zigzag manner near the edge of the semiconductor chip 64. Likewise, the conductive fingers 66 can be lined up along an edge of the substrate 68 or arranged to from a plurality of lines in a zigzag manner. In the example illustrated in FIG. 7, bond pads are arranged in a line near the edge of semiconductor chip 64 and the conductive fingers 66 are arranged to form a plurality of lines in a zigzag manner.
By arranging the conductive fingers 66 to form a plurality of lines in a zigzag manner, bond wires 70 can include short bond wires and long bond wires. Typically, the short bond wires are first bonded to the bond pads 62 and conductive fingers 66. If the long wires are first bonded, the capillary may contact the already bonded long wires when the short wires are bonded to the conductive fingers 66. The maximum diameter of the capillary is typically larger than the width (pitch) of the bond pads 62. Thus, even if there is no contact during the bonding to the bond pad 62, a contact between the bond wire 70 and the capillary can occur when a stitch bond is made to the conductive fingers 66. In view of this problem, the short bond wires 70 are first bonded to connect bond pads 62 to conductive fingers 66. Following this, the long bond wires are bonded to connect bond pads 62 to conductive fingers 66.
However, the conventional bonding method can have the following problems.
A first problem is caused by a probe mark on the surface of a bond pad in generally the same position that the bond wire is to be bonded. The surface of the bond pad in which the probe mark occurs can be rough. If wire bonding is performed on the probe mark, the bond can be unstable. In the conventional example described above, a case is illustrated where bond pads 62 are arranged in a single line. However, even if the bond pads 62 are arranged in a plurality of lines in a zigzag manner, the same problem can occur.
A second problem is that even if the short wires are first bonded to connect the bond pads to the conductive fingers, the capillary can still interfere and contact the short wires when the long wires are bonded.
During the bonding process, a ball (crimp ball) is formed by melting a gold wire with a torch. The capillary then presses the ball against the bond pad. During this process, even if the short wires are formed in advance, the capillary can contact the wires. Typically, there is sufficient space on the side of the conductive fingers so that the capillary rarely creates contact on this side. However, bond pads are arranged along an outer edge of a semiconductor chip in dense manner due to area constraints. When the bond pads are arranged in such a dense manner, there is a high probability that the capillary even interferes and contacts the short wires.
In many cases, the bond wires are arranged in a radial manner around the semiconductor chip. This is because the conductive fingers can have a wider pitch than the pitch of the bond pads. However, if the angle of inclination is increased, as illustrated in FIG. 7, the bond wired may interfere with the moving path of the capillary. Even when there is no difference in the lengths of the bond wires, if the bond wires are arranged in a radial manner (depending on the inclination angles of the bond wires), the capillary can interfere with and contact the bond wires that have been previously formed.
Japanese Patent Publication No. 3,046,630 (in FIG. 1) discloses a semiconductor device in which bond pads include an outer line and an inner line arranged in a zigzag manner. While, such an arrangement may be advantageous from a viewpoint of increasing the density of bond pads, the first above-described problem is not addressed. Namely, the probe marks may still cause unstable or defective bonding.
It should also be noted, that the second above-mentioned problem may not be satisfactorily solved even if the outer line of bond pads are first bonded. On the other hand, if the bond pads in the outer line and the bond pads in the inner line are arranged in a zigzag manner with respect to each other, sufficient space between the bond wire and adjacent bond pads must be provided to ensure that there will be no interference in the bonding process. Thus, the application area of the semiconductor chip may be reduced.
However, even if the bond pads are arranged to form a plurality of lines in a zigzag manner, the capillary may interfere with the bond wires that have been previously formed if the bond pads are densely arranged.
In view of the above discussion, it would be desirable to provide a semiconductor device and wire bonding method. In a wire bonding method, bond pads and bond wires may be connected to each other in succession by using a capillary to supply the bond wire. The bond pads and conductive fingers may be connected to each other while avoiding interference and/or contact between the capillary and already placed bond wires.
It would also be desirable to provide a wire bonding method with which it may be possible to automatically calculate the order of wire bonding in accordance with attributes of bond wires. In this way, the occurrence of interference and contact may be prevented.
It would also be desirable to provide a wire bonding method including a bonding step in which a bond wire may be bonded to a bond pad in an area that may not include a probe mark.